How to move ZVol or Dataset to another pool

Imagine this: your ZFS pool is running out of space, or perhaps you’ve just set up a shiny new storage array with faster drives. Now you’re faced with the challenge of migrating your existing ZVols or datasets to the new pool without downtime or data loss. If you’ve been there, you know it’s not just about running a couple of commands—it’s about doing it safely, efficiently, and with a plan. In this guide, we’ll dive deep into the process of moving ZVols and datasets between ZFS pools, with real-world examples, performance tips, and security considerations to help you avoid common pitfalls.

Understanding the Basics: ZVols, Datasets, and Pools

Before we get into the nitty-gritty, let’s clarify some terminology:

• ZVol: A block device created within a ZFS pool. It’s often used for virtual machines or iSCSI targets.
• Dataset: A filesystem within a ZFS pool, typically used for storing files and directories.
• Pool: A collection of physical storage devices managed by ZFS, which serves as the foundation for datasets and ZVols.

When you move a ZVol or dataset, you’re essentially transferring its data from one pool to another. This can be done on the same system or across different systems. The key tools for this operation are zfs snapshot, zfs send, and zfs receive.

Step 1: Preparing for the Migration

Preparation is critical. Here’s what you need to do before starting the migration:

1.1 Verify Available Space

Ensure the target pool has enough free space to accommodate the ZVol or dataset you’re moving. Use the zfs list command to check the size of the source and target pools:

# Check the size of the source dataset or ZVol
zfs list aaa/myVol

# Check available space in the target pool
zfs list bbb

⚠️ Gotcha: ZFS does not automatically compress data during transfer unless compression is enabled on the target pool. If your source dataset is compressed, ensure the target pool supports the same compression algorithm, or you may run out of space.
1.2 Create a Snapshot
Snapshots are immutable, point-in-time copies of your ZVol or dataset. They’re essential for ensuring data consistency during the transfer. Use the zfs snapshot command to create a recursive snapshot:
# Create a snapshot of a ZVol
zfs snapshot -r aaa/myVol@relocate

# Create a snapshot of a dataset
zfs snapshot -r aaa/myDS@relocate

💡 Pro Tip: Use descriptive snapshot names that indicate the purpose and timestamp, such as @relocate_20231015. This makes it easier to manage snapshots later.
Step 2: Transferring the Data
With your snapshot ready, it’s time to transfer the data using zfs send and zfs receive. These commands work together to stream the snapshot from the source pool to the target pool.
    

        

            

                📚 Continue Reading
            
            

                Sign in with your Google or Facebook account to read the full article.
                
It takes just 2 seconds!
            
            

                
Continue with Google
            
            

                Already have an account? Log in here